Vessel occlusion may be a desirable therapeutic option in the treatment of various diseases of the body. Occlusion of otherwise healthy vessels, sometimes referred to as vessel sacrifice, may be undertaken in conjunction with other therapies, usually to augment these other therapies. For example, in the case of a cancerous tumor, it may be desirable to occlude or sacrifice a tumor feeder vessel in order to disrupt or prevent blood flow to the tumor, with the objective of shrinking the tumor or eliminating it entirely. Though the vessel providing blood flow to the tumor is healthy, it may be worthwhile to sacrifice it in order to prevent growth of the tumor or shrink the tumor. Such a procedure may be undertaken either alone, prior to surgical removal of the tumor, or in conjunction with radiation therapy. As another example, it may be desirable to occlude the internal iliac artery in a patient undergoing aortic or iliac aneurysm repair. The objective of the procedure would be to reduce blood flow into the vessel with the aneurysm, and it would be performed in addition to occlusion of the aneurysm. Another example of desirable vessel sacrifice is the occlusion of the gastroduodenal artery prior to selective internal radiotherapy, to prevent digestive ulcers caused by migration of radioactive particles. In addition to the foregoing examples, there are numerous other therapies in which it may be desirable to sacrifice a blood vessel.
Many devices and methods for the occlusion of or sacrifice of vessels are known in the art. The devices and methods are useful in the cerebral, coronary, and peripheral vasculature. Many known procedures require highly invasive surgery and thus carry many risks. In contrast, endovascular repair compared to open surgery has been reported to reduce early and late morbidity by half. Complications that require invasive or secondary surgical procedures and hospitalization are also reduced with endovascular repair. J Endovasc Ther. 2002 December; 9(6):711-8. Consequently, many of the developments in the art utilize intravascular techniques and devices.
Included among intravascular occlusion devices and methods known in the art are embolic particles, such as coils, that are delivered via intravascular catheter techniques. Embolic particles and coils may be fabricated from metals such as Nitinol, platinum or stainless steel, or polymers, including polymers exhibiting shape memory characteristics. A typical coil is formed by repeated windings of a filament to form a structure of continuous turns, resembling a spring. While use of these coils has had some success, questions remain concerning their long-term effectiveness, ease of use, as well as their potential for post procedure migration of embolic material. Post procedure migration is especially of concern when a treatment site is within a peripheral vessel, which may typically be of larger diameter, and have greater blood flow pressure than the vessels of the coronary or cerebral vasculature.
Other attempts have been made to introduce embolic coils having varied stiffness along the length of the coil, with the objective of achieving more secure anchoring in the vessel. However, most of these attempts are directed to the exterior windings of the wires that form the coil. Drawbacks of these techniques include kinking of the coil during the procedure, sometimes resulting in permanent plastic deformation of the coil Kinking and deformation may interfere with accurate placement of the coil, deployment of the coil, and retraction of the coil back into the delivery catheter. Therefore, there remains a need for reliable, kink free deployment and smooth retraction of vessel occlusion coils. Further, there remains a need in the art for a coil having both sufficient flexibility for vessel safety and sufficient stiffness for vessel occlusion and anchoring of the coil within the vessel.